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Status Report of HERMES

Detailed report on HERMES collaboration's first transversity measurement, exotic baryons like pentaquark, spectrometer overview, & SIDIS cross sections. Operator decomposition, helicity functions, Sivers-Collins effects, and hadron spectroscopy discussed. Monte Carlo simulation, detector calibration, and resonance observations included. Key conclusions on Sivers effects, Collins asymmetries, and ongoing model interpretations presented by Pasquale Di Nezza.

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Status Report of HERMES

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  1. Status Report of HERMES Pasquale Di Nezza (on behalf of HERMES Collaboration) • First measurement of transversity • Exotic baryons: the pentaquark • The spectrometer and the data taking Physics Research Committee, DESY Oct 30/31, 2003

  2. Even they were puzzled … N. Bohr  W. Pauli

  3. DIS + SIDIS cross section

  4. Operator decomposition of the Correlation Function at Twist-2 Unpolarized quark in unpolarized nucleon Helicity difference Function measured by HERMES (EMC,SMC, E142-143-154-155) Extremely well known function

  5. Operator decomposition of the Correlation Function at Twist-2 Single helicity flip NOT ALLOWED IN E.M. INTERACTIONS

  6. Operator decomposition of the Correlation Function at Twist-2 High sensitivity to the valence quark polarization q and q have opposite sign. _ Peculiarity of transversity Relativistic nature of quark. In absence of relativistic effects h1(x)=g1(x) Q2 -evolution. Unlike for g1p(x), the gluon doesn’t mix with quark in h1p(x) Tensor charge: first moment of h1. Calculable by lattice QCD. Double helicity flip Single helicity flip

  7. DIS + SIDIS cross section Peculiarity of • Chiral-even naïve T-odd DF • Related to parton orbital momentum • Violates naïve universality of PDF • - Different sign of in DY (Collins) (Sivers)

  8. Definition of Angles and Asymmetries Angle of hadron relative to initial quark spin (Sivers) Angle of hadron relative to final quark spin (Collins) • Sivers-Collins effects can be distinguished only with transverse polarised target. • Large asymmetry has been measured in inclusive p production (p­ppX) jet axis not known. Both mechanisms involved.

  9. Definition of Angles and Asymmetries

  10. Transverse asymmetry for p+, p-, p0 Sivers Moments Collins Moments • First measurement of naïve • T-odd DF in DIS (orbital mom) • Opposite sign from RHIC DY ? • Much of plausible value ranges of transversity and disfavoured Collins function are excluded

  11. Hadron spectroscopy

  12. Search for Exotic Baryon States • New anti-decuplet NA49 • The 3 corners are exotics Predictions: Bag models (Jaffe ’77; De Swart ’80): 1.8-1.9 GeV Skyrme model (Praszalowicz ’87, Walisser ’92): 1.3 – 1.8 GeV Chiral-Soliton Model (Diakonov, Polyakov ‘97)

  13. Spring-8 Complete Particle Identification with high efficiency: 98% (p), 88% (K), 85% (p) Direct reconstruction: detection of each decay ptc, Inv mass reconstuction (other exp. missing mass) Excellent invariant mass systematics: ± 2 MeV CLAS Saphir CERN, FNAL (n and anti-n) Diana

  14. Event Reconstruction • RICH ID: 1-15 GeV for p, 4-9 GeV for p • Ks decay length>7 cm • Distance cut: p+p-, Ks p, q+ beam • Collinearity Ks pp < 45 mrad • 485< Ks-mass<509 MeV • No L

  15. Particle Identification Proof Good identification of L means clear identification of p Good Ks identification within the kinematical cuts of this analysis

  16. Detector Mass calibration - L(1116) r0(770) f(1020) L*(1520)

  17. Detector Mass calibration - L(1116) r0(770) f(1020) L*(1520)

  18. Detector Mass calibration Masses in agreement with PDG values ± 2 MeV - L(1116) r0(770) f(1020) L*(1520)

  19. Measured Invariant Mass Excess at 1526 MeV Background approximated by a polynomial Width dominated by detector resolution

  20. Monte Carlo Simulation • Simulated resonance at 1540 MeV • Simulated G=2 MeV • Decay in Ksp • Full detector simulation • Recons. Mass at 1540 ± 0.3 MeV • Recons. s=7 ± 0.2 MeV

  21. Status of the Spectrometer

  22. Status of the Spectrometer Spectrometer fully debugged after the shutdownEach single detector is operative!80K DIS collected in 2003-runII with transverse polarized hydrogen target

  23. Conclusions Firstobservation of non-zero Sivers effect Sizeable Collins asymmetries measured for p0 and p- A kind of brain storm is underway for model interpretation 2003: milestone from HERMES transverse asymmetries >2004: results from HERMES, COMPASS, BELLE (RHIC-rIII, CLAS) Pasquale Di Nezza

  24. Conclusions A narrow exotic baryon resonance has been directly reconstructed A kind of brain storm is underway for model interpretation Background description and Monte Carlo simulation { M=1526 ± 2 ± 2 MeV s=7.5 ± 2.4 MeV Most precise determination of the mass Taking data for physics First observation of non-zero Sivers effect Sizeable Collins asymmetries measured for p0 and p- Pasquale Di Nezza

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